1. Field of the Invention
The present invention relates to an improved excavator and a method of forming a modified ground in an earthen foundation with the use of the excavator, and more particularly a method of constructing an underground water cut-off wall, landslide protection wall, a foundation pile or the like, in the earthen foundation.
2. Disclosure of the Prior Art
In the prior art, Japanese Patent Early Publication KOKAI! No. 05-346020 teaches that a modified ground is formed in an earthen foundation by applying a mechanical stirring and an injection of a consolidating fluid. As shown in FIG. 22, this method utilizes an excavator having a rotary shaft 2H. The rotary shaft 2H has a pair of stirring wings 60H which are spaced away from each other axially of the rotary shaft 2H. Each of the stirring wings 60H is provided with a nozzle 15H for jetting the consolidating fluid. The stirring wings 60H are also disposed on the rotary shaft 2H such that the consolidating fluid jetted from one of the nozzles 15H collides with that jetted from the other nozzle.
The modified ground of this prior art is composed of a core pile P1 having a diameter D1 and a ring pile P2 having an outer diameter D2. The core pile P1 is formed by stirring and mixing an excavated soil with the consolidating fluid jetted from a nozzle 14H of the rotary shaft with the stirring wings 60H. At the same time, the ring pile P2 is formed by jetting the consolidating fluid from the nozzles 15H against soil surrounding the core pile P1.
However, when the consolidating fluid jetted from one of the nozzles 15H is intercepted by an obstacle such a rock prior to colliding with that jetted from the other nozzle, it would be difficult to obtain a sufficient mixing and stirring of the consolidating fluid and soil in the ring pile P2, and precisely form the ring pile P2 having the diameter D2.
In addition, a mixing state of the excavated soil with the consolidating fluid in the core pile P1 would be different from the mixture state in the ring pile P2 because the soil in the core pile P1 is mixed with the consolidating fluid mainly by the stirring wings 60H, and on the other hand the soil in the ring pile P2 is excavated mainly by the consolidating fluid jetted from the nozzles 15H without utilizing the stirring wings 60H. As a result, it would be difficult to uniformly form the modified ground as a whole in the earthen foundation.
Moreover, when a joined jet of the consolidating fluid, which is generated by collision of the consolidating fluid jetted from the nozzles 15H, advances in a horizontal or upwardly diagonal direction, there is a probability of causing upheavals on the ground or blowing the soil to the outside of the modified ground by the joined jet. In particular, when thus blown soil hits the worker, it would give a serious injury to the worker.